Brake force regulators for dual circuit brake systems in both brake circuits are known as illustrated in the German unexamined patent application DT-OS No. 2,236,294. In the prior art brake force regulator, the regulated pressure of one brake circuit in front of the larger stepped-piston end is transferred to a closing member of a pressure reducer by means of a floating intermediate piston. This provides structure in which the regulated pressure of the brake circuit connected with the pressure reducer always follows the regulated pressure of the brake circuit connected with a brake force limiter only when both brake circuits are intact. Thus, the simple pressure reducer in each brake circuit operates as a brake force regulator only so long as both brake circuits are intact. However, if the brake circuit which includes the brake force regulator fails, the device of German unexamined patent application DT-OS No. 2,236,294, does not operate satisfactorily because no further brake pressure can be built up in the wheel cylinders connected to the pressure reducer when the single switching point has been reached.
When it is recognized that rear-axle brakes may also be designed to include dual circuit brakes, an increased or higher switching point with subsequent normal brake force regulation would be an extremely desirable feature.
It is known, as illustrated in German patent DT-OS No. 1,915,485, that a device can be provided which will combine two load-conscious brake-force limiters such that a genuine dual circuit design is maintained. This is achieved by a mechanical transfer of the axle load determined control force, which predetermines the closing point from one brake force limiter to the other. Not only does the device illustrated in German patent DT-OS No. 1,915,485 not allow for any brake force regulation, it also does not make it possible to vary the closing point by a specific degree, which is predetermined by the design, if a brake circuit fails.